Esterases and lipases both hydrolyse ester bonds. Whereas the lipases display high activity towards the aggregated state of its substrate, the esterases typically show highest activity towards the soluble state of its substrate. We have compared the amino acid sequence, the 3D-structure as well as the pH-dependent electrostatic signature of selected members of the two families, for which 3D-structural information is publicly available. Lipases display a statistically significant enhanced occurrence of non-polar residues close to the surface, clustering around the active-site. Lid opening appears to strengthen this pattern further. As we have proposed earlier the active site of lipases displays negative potential in the pH-range associated with their maximum activity, typically at pH values above 8. The esterases show a very similar pattern, however, at pH values around 6 correlated with their usually lower pH-activity optimum.